The ‘hydrogen economy’ requires a lot of things, but first is an easy and cheap supply of hydrogen. There are lots of ways to make it, but most of them don’t produce large quantities quickly or inexpensively. Professor Bruce Logan, director of the Hydrogen to Energy Center at Penn State University, has found a way to change that. He used a process called reverse electrodialysis, combined with some ordinary bacteria to get hydrogen out of water by breaking up its molecules. Water — which is made of two atoms of hydrogen and one of oxygen — can be broken down with electricity. (This is a pretty common high school science experiment). The problem is that you need to pump a lot of energy into the water to break the molecules apart.

Logan thought there had to be a better way. He combined two methods of making electricity — one from microbial fuel cell research and the other from reverse electrodialysis. In a microbial fuel cell, bacteria eat organic molecules and during digestion, release electrons. In a reverse electrodialysis setup, a chamber is separated by a stack of membranes that allow charged particles, or ions, to move in only one direction. Filling the chamber with salt water on one side and fresher water on the other causes ions to try and move to the fresher side. That movement creates a voltage. Adding more membranes increases the voltage, but at a certain point it becomes unwieldy. By putting the bacteria in the side of the reverse electrodialysis chamber with the fresh water, and using only 11 membranes, Logan was able to generate enough voltage to generate hydrogen. Ordinarily he would need to generate about 0.414 volts. With this system, he can get .8 volts, nearly double. (The microbial part of the cell generates 0.3 volts and the RED system creates about 0.5.)

Using seawater, some less salty wastewater with sewage or other organic matter in it and the bacteria, Logan’s apparatus can produce about 1.6 cubic meters of hydrogen for every cubic meter of liquid through the system of chambers and membranes. Another bonus is that less energy goes into pumping the water — if anything, flow rates and pressure have to be kept relatively low so as not to damage the membranes. Making hydrogen cheaper is a necessity if hydrogen cars are to be a reality. Some car companies already make hydrogen-powered models. The state of Hawaii is already experimenting with hydrogen fuel systems. Producing cheaper, abundant hydrogen — especially from sewer water and seawater — is a big step in that direction.

US researchers say they have demonstrated how cells fueled by bacteria can be “self-powered” and produce a limitless supply of hydrogen. Until now, they explained, an external source of electricity was required in order to power the process. However, the team added, the current cost of operating the new technology is too high to be used commercially. Details of the findings have been published in the Proceedings of the National Academy of Sciences.

“There are bacteria that occur naturally in the environment that are able to release electrons outside of the cell, so they can actually produce electricity as they are breaking down organic matter,” explained co-author Bruce Logan, from Pennsylvania State University, US. “We use those microbes, particularly inside something called a microbial fuel cell (MFC), to generate electrical power. “We can also use them in this device, where they need a little extra power to make hydrogen gas. “What that means is that they produce this electrical current, which are electrons, they release protons in the water and these combine with electrons.”

Prof Logan said that the technology to utilize this process to produce hydrogen was called microbial electrolysis cell (MEC). “The breakthrough here is that we do not need to use an electrical power source anymore to provide a little energy into the system. “All we need to do is add some fresh water and some salt water and some membranes, and the electrical potential that is there can provide that power.” The MECs use something called “reverse electrodialysis” (RED), which refers to the energy gathered from the difference in salinity, or salt content, between saltwater and freshwater.

In their paper, Prof Logan and colleague Younggy Kim explained how an envisioned RED system would use alternating stacks of membranes that harvest this energy; the movement of charged atoms move from the saltwater to freshwater creates a small voltage that can be put to work. “This is the crucial element of the latest research,” Prof Logan told BBC News, explaining the process of their system, known as a microbial reverse-electrodialysis electrolysis cell (MREC). “If you think about desalinating water, it takes energy. If you have a freshwater and saltwater interface, that can add energy. We realized that just a little bit of that energy could make this process go on its own.”

He said that the technology was still in its infancy, which was one of the reasons why it was not being exploited commercially. “Right now, it is such a new technology,” he explained. “In a way it is a little like solar power. We know we can convert solar energy into electricity but it has taken many years to lower the cost. “This is a similar thing: it is a new technology and it could be used, but right now it is probably a little expensive. So the question is, can we bring down the cost?” The next step, Prof Logan explained, was to develop larger-scale cells: “Then it will easier to evaluate the costs and investment needed to use the technology. The authors acknowledged that hydrogen had “significant potential as an efficient energy carrier”, but it had been dogged with high production costs and environmental concerns, because it is most often produced using fossil fuels.

Prof Logan observed: “We use hydrogen for many, many things. It is used in making [petrol], it is used in foods etc. Whether we use it in transportation… remains to be seen.” But, the authors wrote that their findings offered hope for the future: “This unique type of integrated system has significant potential to treat wastewater and simultaneously produce [hydrogen] gas without any consumption of electrical grid energy.” Prof Logan added that a working example of a microbial fuel cell was currently on display at London’s Science Museum, as part of the Water Wars exhibition.

A grain of salt or two may be all that microbial electrolysis cells need to produce hydrogen from wastewater or organic byproducts, without adding carbon dioxide to the atmosphere or using grid electricity, according to Penn State engineers. “This system could produce hydrogen anyplace that there is wastewater near sea water,” said Bruce E. Logan, Kappe Professor of Environmental Engineering. “It uses no grid electricity and is completely carbon neutral. It is an inexhaustible source of energy.” Microbial electrolysis cells that produce hydrogen are the basis of this recent work, but previously, to produce hydrogen, the fuel cells required some electrical input. Now, Logan, working with postdoctoral fellow Younggy Kim, is using the difference between river water and seawater to add the extra energy needed to produce hydrogen. Their results, published in the Sept. 19 issue of the Proceedings of the National Academy of Sciences, “show that pure hydrogen gas can efficiently be produced from virtually limitless supplies of seawater and river water and biodegradable organic matter.”

Logan’s cells were between 58 and 64 percent efficient and produced between 0.8 to 1.6 cubic meters of hydrogen for every cubic meter of liquid through the cell each day. The researchers estimated that only about 1 percent of the energy produced in the cell was needed to pump water through the system. The key to these microbial electrolysis cells is reverse-electrodialysis or RED that extracts energy from the ionic differences between salt water and fresh water. A RED stack consists of alternating ion exchange membranes — positive and negative — with each RED contributing additively to the electrical output. “People have proposed making electricity out of RED stacks,” said Logan. “But you need so many membrane pairs and are trying to drive an unfavorable reaction.” For RED technology to hydrolyze water — split it into hydrogen and oxygen — requires 1.8 volts, which would in practice require about 25 pairs of membranes and increase pumping resistance. However, combining RED technology with exoelectrogenic bacteria — bacteria that consume organic material and produce an electric current — reduced the number of RED stacks to five membrane pairs.

Previous work with microbial electrolysis cells showed that they could, by themselves, produce about 0.3 volts of electricity, but not the 0.414 volts needed to generate hydrogen in these fuel cells. Adding less than 0.2 volts of outside electricity released the hydrogen. Now, by incorporating 11 membranes — five membrane pairs that produce about 0.5 volts — the cells produce hydrogen. “The added voltage that we need is a lot less than the 1.8 volts necessary to hydrolyze water,” said Logan. “Biodegradable liquids and cellulose waste are abundant and with no energy in and hydrogen out we can get rid of wastewater and by-products. This could be an inexhaustible source of energy.” Logan and Kim’s research used platinum as a catalyst on the cathode, but subsequent experimentation showed that a non-precious metal catalyst, molybdenum sulfide, had 51 percent energy efficiency.

Humans should have a little more respect for dirty toilet water. In recent years, wastewater has become something of a commodity, with nuclear plants paying for treated wastewater to run their facilities, cities relying on so-called “toilet to tap” technology, and breweries turning wastewater into biogas that can be used to power their facilities. Soon enough, wastewater-powered batteries may even keep the lights on in your house or, at the very least, in the industrial plants that clean the wastewater.

Environmental engineer Bruce Logan is developing microbial fuel cells that rely on wastewater bacteria’s desire to munch on organic waste. When these bacteria eat the waste, electrons are released as a byproduct–and Logan’s fuel cell collects those electrons on carbon bristles, where they can move through a circuit and power everything from light bulbs to ceiling fans. Logan’s microbial fuel cells can produce both electrical power and hydrogen, meaning the cells could one day be used to juice up hydrogen-powered vehicles.

Logan’s fuel cells aren’t overly expensive. “In the early reactors, we used very expensive graphite rods and expensive polymers and precious metals like platinum. And we’ve now reached the point where we don’t have to use any precious metals,” he explained to the National Science Foundation. Microbial fuel cells still don’t produce enough power to be useful in our daily lives, but that may change soon–Logan estimates that the fuel cells will be ready to go in the next five to 10 years, at which point they could power entire wastewater treatment plants and still generate enough electricity to power neighboring towns. There may also be ones that use–and in the process-desalinate–salt water, using just the energy from the bacteria. And if the microbial fuel cells don’t work out, there’s another option: Chinese researchers have developed a photocatalytic fuel cell that uses light (as opposed to microbial cells) to clean wastewater and generate power. That technology is also far from commercialization, but in a few years, filthy water will power its own cleaning facilities one way or another.